Conveyors with endless, flexible conveying elements are commonly used for the movement of manufactured packages or packing container blanks between different machines. In the manufacture of non-returnable packages e.g. milk or juice, conveyors are used for transferring the finished packing containers to machines for application of suction tubes, wrapping in shrink film etc. The conveying elements of the conveyors consist of hinged chain segments which run on a support beam and are surrounded by guide rails placed on either side of the conveying element and at different height above the same. The distance between the guide rails is chosen so that, within certain limits, packing containers of different dimensions can be conveyed unhindered without adjustment of the guide rails when the package size is altered. At the points where the conveyor bends, however, the distance between the guide rails has to be increased so that the packing containers do not catch if their length in the direction of transport is greater than their width. As it is also desirable to prevent blockage of the conveyor in cases where a packing container has overturned and is conveyed in a horizontal position through the curve (that is to say, seen in the direction of transport, taking up an appreciably greater length than normal), the distance between the guide rails has to be considerably greater in the curves than in the straight portions of the conveyor. In 90.degree. curves, for example, the distance between the guide rails has to be almost doubled so as to prevent a horizontal packing container from being jammed between the guide rails owing to the increased length when it is to pass the curve. The increased width between the guide rails brings with it inferior guidance of the packing containers which means an increased risk of their turning in an undesirable manner during the passage around the curves. To prevent this it has been suggested to supplement the inner guide rails in the curves with a further steering rail which limits the free width, but which is situated above the guide rails and, more particularly, at such a height that a packing container which has overturned and is thus conveyed in horizontal position can pass unhindered under the steering rail and thereby pass the curve without getting caught.
It has been found that by this principle the risk of undesirable turning of the packing containers in the curves is substantially reduced. However, if the function is to remain as desired an accurate adjustment and adaptation of the steering rail to each individual package size is required.